The invention relates to catalysts with an alumina, silica or silica-alumina base, their manufacture and their use, particularly for hydrotreating hydrocarbon oils, specially oils from petroleum, petroleum fractions or coal hydrogenation.
The catalysts which are conventionally used in the domain of hydrorefining oil or oil fractions comprise a carrier such as alumina, silica or silica-alumina and at least one metal or compound of a metal from group V and/or VI and/or VIII, particularly vanadium, mobybdenum, tungsten, nickel, cobalt, iron or the noble metals. Alumina (or silica) can be pure or comprise additional components, depending on the expected use, for example alkali metals or alkaline-earth metals, rare earth metals, silica (or alumina), magnesia, thoria, halogen, in a proportion which can reach 10%, sometimes 30% or more. To simplify, all these materials will be called "support material" in the following disclosure.
These catalysts may appear under various shapes, for example powder, spherical or ovoid balls, extrudates of circular or polylobal cross-section, pellets. For use in fixed, moving or expanded bed, it is usual to employ balls having diameters between 1 and 4 mm.
These balls can be manufactured by agglomerating powder of support material according to a number of known techniques, for example in a revolving bowl-granulator or in hot oil by the method of drop coagulation ("oil up" and "oil drop"), optionally after addition of poreforming agents well known in the art. The resultant balls are then calcined at 300.degree.-1000.degree. C.
Whenever necessary, agents for forming the balls or for maintaining their strength are added to the powder to be agglomerated or to the wetting liquid. These additives which can be, for example, easily rehydratable alumina, alumina or silica gel diluted with water, nitric acid, etc., are well known in the art.
The balls are then "matured", i.e. maintained in a wet atmosphere at a moderate temperature, for example between about 60.degree. and about 100.degree. C., then dried at about 100.degree. to 200.degree. C. and calcined at about 300.degree. to 1000.degree. C. (activation treatment).
Another method for manufacturing balls consists of using the technique known in the art as "oil drop" or "oil up", which consists of introducing a fluid paste based on silica, alumina or silica-alumina into a reactor filled with a generally hot, conveniently selected liquid. This fluid paste is shaped into small particles by passage through an injector of convenient diameter. These particles can be injected at the bottom of the reactor (oil up) and move upwardly, as a result of the differential density, through the hot liquid, while forming substantially spherical balls. They can also be injected (oil drop) at the top of the reactor and flow downwardly by gravity while forming balls. The resulting products are then generally dried and calcined, for example at 300.degree.-1000.degree. C.
The calcined balls can then be used as catalyst carrier: they are impregnated with a solution of the catalytic elements or their precursors. However, the catalytic elements or their precursors can be introduced into the alumina powder and the resultant mixture subjected to the above operations of shaping, drying and calcining, for example at 300.degree.-1000.degree. C.
For certain applications, when the balls comprise alumina, it can be advantageous to subject the calcined balls to a subsequent treatment with water or steam, called "autoclaving", at a temperature comprised between about 80.degree. C. and about 300.degree. C. for about 5 minutes to 48 hours, preferably 1 to 6 hours.
The aqueous "autoclaving" medium preferably contains at least one acid able to dissolve a portion of the alumina of the agglomerates, or a mixture of such an acid with at least one compound supplying an anion able to combine with the aluminum ions, for example a mixture of nitric acid with acetic or formic acid.
The balls obtained from the "autoclaving" are then dried and activated by heating at a temperature of about 300.degree. to 1000.degree. C.
The above "autoclaving" technique is disclosed, for example, in the French Pat. No. 2,496,631.
When using the "autoclaving", the catalytic materials or their precursors can be introduced either before agglomeration of the alumina powder or after the calcination following this agglomeration, as shown above, or preferably after the "autoclaving" treatment and the subsequent thermal activation. In the latter case, after introduction of the catalytic elements, the material is dried and calcined at 300.degree.-1000.degree. C. and/or reduced, according to known techniques.
The resultant balls have usually a surface of 50 to 350 m.sup.2 /g, preferably 100 to 250 m.sup.2 /g and a total pore volume of 0.4 to 1.5 cc/g, preferably 0.8 to 1.2 cc/g.
The autoclaving treatment and/or the thermal treatments modify the structure of the alumina and/or silica and their characteristics, specially the specific surface and the porosity, this modification being useful for certain catalytic uses, among which is hydrorefining. More particularly, the autoclaving treatment, particularly when performed in acid medium, confers upon the hydrorefining catalysts of the type disclosed above, containing alumina, an outstanding resistance to poisoning by metal and/or asphaltenes fouling.